1. Field of the Invention
The present invention relates to a speaker including a bimorph vibrator.
2. Description of the Related Art
The structure of a conventional speaker including a bimorph vibrator will be explained with respect to FIG. 6 and FIG. 7.
In FIG. 6 and FIG. 7, a speaker 1 includes a vibrator 2 supported on and secured to a supporting member 5 with a cushioning material 6 disposed between the vibrator 2 and the supporting member 5. The vibrator 2 is a bimorph vibrator and includes a first piezoelectric element 4a and a second piezoelectric element 4b, which are respectively bonded by an adhesive to a first main surface 3a and a second main surface 3b of a dish-shaped metal plate 3. The first and second piezoelectric elements 4a and 4b include a dish-shaped body made of a piezoelectric material, such as ceramic, and are polarized in a direction that is parallel to the thickness thereof.
Furthermore, the cushioning material 6 is made of a flat plate-shaped elastic material, such as rubber. The supporting member 5 is made of a ring-shaped synthetic resin or the like, and has a ring-shaped step portion 5a on one main surface 51 thereof. The supporting member 5 includes a through-hole 5b, running from the inner wall 52, passing below the step 5a and extending to the main surface 51.
The cushioning material 6 is securely affixed to the step 5a of the supporting member 5 via an adhesive (not shown in FIG. 6 or FIG. 7). Moreover, a portion near the rim 3c of one main surface 3a of the metal plate 3, which forms the vibrator 2, is affixed to the top surface of the cushioning material 6 via an adhesive 7, which is made of an elastic material such as silicon or urethane, whereby the vibrator 2 is supportively secured on the supporting member 5.
Furthermore, electrodes 9a and 9b are provided respectively on the surfaces of the first and second piezoelectric elements 4a and 4b, which form the vibrator 2, thereby providing a driving element for vibrating the vibrator 2. Ends of conducting wires 10a and 10b are connected via solder members 11a and 11b to the electrodes 9a and 9b, and other ends of the conducting wires 10a and 10b are connected to an input terminal (not shown in FIG. 6 or FIG. 7) of the speaker 1. The conducting wire 10b passes through the through-hole 5b, provided in the supporting member 5, and extends outside of the supporting member 5.
In the speaker 1 having the construction described above, when an electrical signal is input to the input terminal, the vibrator 2 vibrates, whereby sound waves are emitted from the outer surface of the vibrator 2.
However, in the conventional speaker 1, since the portion near the rim 3c of the main surface 3a of the metal plate 3, which forms the vibrator 2, is securely affixed to the surface of the flat plate-like cushioning material 6, it is very difficult to position the vibrator 2 during assembly, and there is a danger that the vibrator 2 will deviate from its predetermined, desired position on the supporting member 5.
Furthermore, the bond between the metal plate 3 and the cushioning material 6, achieved by the adhesive 7, may become loose due to the large amplitude of the vibrator 2, especially when the speaker 1 is used in a woofer of acoustic equipment, and as a result, the vibrator 2 is separated or peels away from the cushioning material 6. Similarly, there is a danger that the vibrator 2 will peel away from the cushioning material 6 when the vibrator 2 has expanded or shrunk due to application of heat.
To overcome the problems described above, preferred embodiments of the present invention provide a speaker in which a vibrator is easily positioned during assembly of the speaker and the vibrator is not separated from and does not peel away from a cushioning material provided on a supporting member which supports the vibrator.
According to a preferred embodiment of the present invention, a speaker includes a vibrator having a first piezoelectric element bonded to a first main surface of a metal plate and a second piezoelectric element bonded to a second main surface of in the metal plate, a supporting member having a step portion, and a cushioning material provided in the step portion of the supporting member. The speaker is preferably formed by affixing the metal plate to the cushioning material using an adhesive member, and supportively securing the vibrator on the supporting member, wherein a step is provided in the cushioning material, clipping the rim of the metal plate and a portion near the rim of a first main surface into the step provided in the cushioning material, and both or either one of the rim of the metal plate and the portion near the rim of the first main surface being affixed to the step of the cushioning material using an adhesive member.
Preferably, in this preferred embodiment, a reinforcing member is provided at a portion extending over a second main surface of the metal plate, the adhesive member and the cushioning material, or a portion extending over the second main surface of the metal plate and the adhesive member.
In this case, the same material used to form the adhesive member is preferably used to form the reinforcing member.
According to the speaker of preferred embodiments of the present invention, a step is provided in a cushioning material which is secured to a supporting member, and a side of a first main surface a metal plate which defines a vibrator, clips into the step, thereby making it very easy to position the vibrator during assembly of the speaker.
Furthermore, the vibrator is more strongly secured to the cushioning material by providing an adhesive member at a portion of the second main surface of the metal plate, which extends over the vibrator, the adhesive member and the cushioning material, or alternatively, a portion of the second main surface of the metal plate, which extends over the vibrator, and therefore, when the vibrator vibrates with comparatively large amplitude, or when the vibrator expands or shrinks due to heat, separation and peeling of the vibrator from the cushioning material is prevented.
When the same material used to form the adhesive member which affixes the cushioning material to the first main surface of the metal plate which defines the vibrator, is provided to define the reinforcing device, since these adhesive members have the same thermal expansion coefficient, they do not crack when they expand or shrink due to heat.
For the purpose of illustrating the invention, there is shown in the drawings. several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.